Basement membrane is a dense, highly cross-linked form of extracellular matrix that surrounds most tissues. During development and immune surveillance, specialized cells acquire the ability to breach basement membrane to disperse and traffic to sites of infection and injury. The cell invasion program is also co-opted or misregulate during many diseases, including asthma, arthritis, the pregnancy disorder pre-eclampsia, and cancer. Understanding how cells invade through basement membrane is thus of great importance to human health. Cell invasion involves dynamic interactions between the invading cell, the tissue being invaded, and the basement membrane separating them. Owing to an inability to recapitulate these complex interactions in vitro, and the challenge of experimentally examining invasion in vivo, the key mechanisms underlying cell invasive behavior remain poorly understood. Anchor cell invasion in C. elegans is an experimentally accessible in vivo model of cell invasion that uniquely combines single cell visual analysis with powerful genetic and genomic approaches. Using these strengths, we have identified two conserved transcription factors that regulate distinct steps in acquiring an invasive cell fate. NHR-67, an ortholog of the vertebrate Tailless protein, maintains the anchor cell in a post-mitotic state. Exit from the cell cycle appears necessary to then permit the C. elegans Fos family transcription factor ortholog FOS-1A to initiate the invasion program. Preliminary data indicate that FOS-1A regulates the expression of three matrix metalloproteinases (MMPs) in the anchor cell, implicating a specific pathway that controls basement membrane removal. Finally, we have found that elevated levels of the extracellular matrix protein SPARC, which is overexpressed in most advanced cancer malignancies, decreases type IV collagen levels in basement membrane, and dramatically enhances anchor cell invasion. The goal of this proposal is to use live-cell imaging with genetic and molecular analysis to determine: (1) How NHR-67 maintains the anchor cell in a post-mitotic state and allows the cell invasion program to initiate, (2) the role of FOS-1A in regulatin MMP expression and the function of MMPs in breaching the BM, (3) the role of SPARC in enhancing cell invasion. These studies are relevant to NIH's mission as they will lead to new insights into the importance of cell cycle exit for invasion, the specific role of MMPs in breachin basement membrane and the role of SPARC in facilitating the invasive process, thus allowing the development of better therapeutic strategies to limit invasive behavior in human diseases such as cancer.